C.-W. Chung et al. (Eds.): HSI 2003, LNCS 2713, pp. 719-724, 2003. Springer-Verlag Berlin Heidelberg 2003

A Study on Mobile Commerce AAA Mechanismfor Wireless LAN*

Gwanyeon Kim1, Chinu Lee1, Sehyun Park1 **, Ohyoung Song1, and ByunghoJung2

1 School of Electrical and Electronic Engineering, Chung-Ang UniversitySeoul Korea

{cityhero,alelee}@ms.cau.ac.kr{shpark,song}@cau.ac.kr

http://bkmodem.cau.ac.kr/main.htm2 Electrics and Telecommunications Research Institute

cbh@etri.re.krhttp://www.etri.re.kr

Abstract. Wireless LAN is rapidly becoming a crucial component inthe next generation mobile communication. In spite of this success,user’s privacy and access control like the authentication problems alongwith the Accounting and the Billing problems are arising. Especially inthe accounting field, the research for the packet accounting based on IPis insufficient so that several ISP’s adopted a fixed sum system for theaccounting. This paper presents a packet accounting model compatiblewith the International Standards for mobile commerce and the verifica-tion results.

1 Introduction

IMT-2000, 3G mobile communication, is suffering difficulty in the market entry dueto the expensive hand-held device, the service rate and the delayed commercial serv-ice. Therefore the IMT-2000 service providers are attempting to cooperate with thewireless LAN service providers for the market entry and the profitability.

In the wireless LAN, user’s privacy and access control like the authenticationproblems along with the Accounting and the Billing problems are arising. Also, theauthentication, the access control and the accounting process, and the interoperabilitywith the next generation mobile communication are very complicate to implement.

Consequently, this paper presents a packet-based accounting model for mobilecommerce compatible with the International Standards and the simulation results ofthis accounting model. The proposed model is applied in the wireless LAN that isconsisted of the IEEE 802.11b[1] networks, and to guarantee the compatibility and

* This research was supported by the Chung-Ang University Research Grants in 2002.** The corresponding author.

720 Gwanyeon Kim et al.

the interoperability, we develop Diameter-based packet accounting model. We usedIAPP (Inter Access Point Protocol)[2] and the prepaid accounting system for theeffective accounting and to improve the mobility. The next section, we examine theAAA model for the public wireless LAN.

2 AAA Protocol for the Wireless LAN

2.1 Radius Protocol

The best-known and most widely deployed AAA Protocol is RADIUS (Remote Ac-cess Dial-In User Service)[3][7]. It was developed in the mid-1990s by LivingstonEnterprises (since acquired by Lucent) to provide authentication and accountingservices to their NAS (Network Access Server) device.

2.2 Diameter Protocol

RADIUS continues to enjoy widespread support among ISP and enterprise networkmanagers. However, was originally engineered for small network devices supportingjust a few end-users requiring simple server-based authentication. Dial providers mustnow provide AAA services for hundreds users accessing network services over avariety of technologies. Therefore, the IETF has undertaken an effort to develop anext-generation AAA protocol which is Diameter Protocol [4][7].

3 AAA Protocol for Wireless LAN in Mobile Environment

It must be researched and developed comprehensive and systematic AAA model thatsupports the roaming and the various charging system to apply wireless LAN over theMobile Commerce. Therefore, in this paper, we provides Diameter-based AAAmodel for wireless LAN. The following section is about the accounting system withimproved mobility over the wireless LAN system.

3.1 Extended IAPP for Mobility Support

For the special quality of electric wave, the radius of AP (Access Point) is about 100to 300 meters. For that reason, handover between APs occur frequently. Therefore,the authentication process between AP and AAA server happens for each handoverand a new accounting session is created. Because of the authentication and the ac-counting process, the network traffics are increased and the user’s connection is inter-rupted and the efficiency of server is decreased. Therefore, the cost of service is in-creased.

Applying the proposed extended IAPP, the AP does not request an authenticationprocess to an authentication server and uses the authentication and accounting infor-mation of the previous AP while handover occurs. Therefore, the mobile terminalreceives the service immediately.

A Study on Mobile Commerce AAA Mechanism for Wireless LAN 721

So, these characteristics guarantee the mobility between domains and betweennetworks. Fig. 1 shows the extended IAPP protocol.

M NO ldAP

N ewAP

O ld AAAServer

E A P O L.S tart

E A P - S uccess(A P IP , Token)

E A P O L.S tart(O ld A P IP , Token)

IA P P - M ove.R equest(Token)

IA P P - M ove.R esponse(C onText)

E A P - S uccess

EVEN T : H andoff (oAP -> nAP)

D ata E xchange

D ata E xchange

AAAServer

E A P P acket Transfer

A ccounting S ession(S ession.ID )

A uthentication

A ccounting S ession(S ub_S ession.ID )

①

②

③

④

⑤

⑥

Fig. 1. Extend IAPP Protocol

3.2 Diameter-Based Packet Accounting Model

The packet-based accounting model proposed in this paper is divided in prepaid andpostpaid accounting systems. The postpaid accounting model is out of the subject andwe will not handle in this paper.

The billing server sends the number of available packet computed previously toAAA server. So the transaction is decreased between the billing server and AAAserver. Also, the accounting policy and the service fee table must be discussed previ-ously due to the user’s roaming between the different service providers. Fig. 2 illus-trates the proposed accounting system.

AP

M N

FAAA H AAA

D B

B illingServer

H om e D om ainForeign D om ain

Fig. 2. Proposed AAA Architecture

The following paragraphs explain the prepaid accounting procedures in five cases.

(1) Case 1: Prepaid User Authentication

AAA server must sends the accounting information to user and the authentica-tion must set to Full service of Limited service according to accounting infor-mation.

(2) Case 2: Balance Notification, Warning, Expiration

722 Gwanyeon Kim et al.

The HAAA renews the user’s balance in the real time based on the amount ofdata sent and received by the user and notifies it to the user. When the balancereaches some fixed limits in advance, the HAAA gives a warning message sothat the user can make provisions for termination of the service. Finally, in thecase that the balance is expired, the status is switched from Full Service to Lim-ited Service. A balance notification, warning, expiration procedure is shown inFig. 3.

M N AP H AAAFAAA

Interim A ccounting(U ID , U sedPacket)

(2)

(5)

B alance Expiration (U ID ,

A vailablePacket=0, Service=LIM ITED )

(Lim ited Service)

B alance N otification(U ID , A vailablePacket)

Session Initial

~ ~ ~ ~

Interim A ccounting

(U ID , U sedPacket)

(8)B alance w arning

(U ID , A vailablePacket, W arningText)

Interim A ccounting

(U ID , U sedPacket)

(6)

(7)

(9)

(10)

(11)

(12)

~ ~~ ~

~ ~ ~ ~~ ~~ ~

~ ~ ~ ~~ ~~ ~

~ ~ ~ ~~ ~~ ~

~ ~ ~ ~~ ~~ ~

(1)

(4)(3)

B alance w arning

B alance N otification

B alance Expiration

Fig. 3. Balance Notification, Warning, Expiration Procedure

(3) Case 3: Balance Recharge

If the user recharges his or her balance, the Billing Server calculates the numberof packets corresponding to the recharged balance and transmits it to the AAAserver. The AAA server renews the number of packets and adds the remainingones to the newly recharged ones. The balance recharging procedure is depictedas shown in Fig. 4.

M N AP H AAAFAAA B illing Server

(U ID , nA vailablePacket)B alance R echarge

(U ID , A vailablePacket=

oA vailablePacket+nA vailablePacket)(Full Service)

(5)Interim A ccounting

(U ID , U sedPacket)

(2)

(3)

(4)

EVEN T : B alance R echarge(1)

B alance R echarge

B alance R echarge

Fig. 4. Balance Recharge Procedure

(4) Case 4: Rate Change

The rates vary according to QoS levels and time of day used. The Billing Serverconverts the remaining number of packet into money and computes the numberof packets again in accordance with the new list of charges and transmits it sothat the user can get the service continuously. The rate change procedure isshown in Fig. 5.

A Study on Mobile Commerce AAA Mechanism for Wireless LAN 723

H AAA B illing Server

R ate C hange R equest

R ate C hange

B alance Packet R equest

(U ID , A vailablePacket)

(2)

(1)

(4)

(3)

B alance Packet R esponse(U ID , A vailablePacket)

Fig. 5. Rate Change Event

(5) Case 5: Roaming

This case is similar to the rate change procedure of the previous case (Case 4)and is that the Rate Table is changed according to the global roaming.

4 Performance Evaluation

Let’s assume that a1, a2, a3, a4 represent a wireless LAN section, a private line sec-tion, an Ethernet section, a fast private line section respectively on the basis of net-work bandwidth and that the transmission delay of each section is defined in terms ofa4 as follows: a1 = 14 * a4, a2 = 100 * a4 and a3 = 10 * a4.

We change renewal times per minute with respect to the Rate Table (rate_n) from1 to 60 and fix the value of other parameters. Since 60 times of Interim Accountingper minute and the same times of balance notification per minute occur subsequently,2 times of transaction per second take place from the MN to the Billing Server. Thus,the transmission delay can be expressed in the following form.

60sec * 2 times * (a1+a2+a3+a4) (1)

In the proposed model, on the other hand, transaction times from the MN to theAAA server are the same with above but transaction to the Billing Server is propor-tional to the number of times of the rate change. Therefore, the transmission delay inthe proposed model can be written as follows:

60sec * 2 times *(a1+a2+a3) +2 times *rate_n*a4 (2)

We can get the difference (120-2*rate_n)*a4 from two equations above. Thus, thisshows the higher performance improvement in the small rate_n and the results of twomodels are the same if rate_n=60.

Table 1 compares the existing scheme (Case 1) with the proposed scheme (Case2), and a graph for the performance analysis of case 1 and 2 is depicted as shown inFig. 6.

Table 1. Delay Relation Compare Table

rate_n 1 4 8 12 24

724 Gwanyeon Kim et al.

Case 1 15000×a4 15000×a4 15000×a4 15000×a4 15000×a4Case 2 14882×a4 14888×a4 14896×a4 14906×a4 14924×a4

14820

14840

14860

14880

14900

14920

14940

14960

14980

15000

15020

1 4 8 12 24

C ase 1

C ase 2

a4

rate_n

Fig. 6. Performance Graph

5 Conclusions

In this paper we presented AAA protocol to provide 802.11-based wireless LAN,authentication, privilege and accounting services also, technologies to support themobility. Finally, we proposed and verified a packet-based accounting model thatsatisfies the requirements for the prepaid/postpaid accounting service, and supportsthe mobility for the global roaming as well. The proposed prepaid packet-based ac-counting model provides real time accounting service and management of the bal-ance. Also, authentication method for prepaid user is applied in this model.

References

[1] "8802-11 Part 11: Wireless LAN Medium Access Control (MAC) and PhysicalLayer (PHY) specifications", ISO/IEC

[2] David Bagby et. al., "Draft Recommended Practice for Multi-Vendor AccessPoint Interoperability via an Inter-Access Point Protocol across DistributionSystems Supporting IEEE 802.11 Operation", internet draft, January 2003

[3] Rigney et. al., "Remote Authentication Dial In User Service", IETF, RFC2865,April 1997

[4] Pat R. Calhoun et. al., "Diameter Base Protocol", IETF Internet Draft, Decem-ber 2002

[5] Perkins. C, "IP Mobility Support for IPV4 revised", IETF, RFC3220, January2002

[6] Mick Seaman et. al., "Port-Based network Access Control", IEEE, June 2001[7] Metz. C, "AAA protocol: Authentication, Authorization, and Accounting for

the Internet", IEEE computing, IEEE, Vol3 Issue 6, Nov/Dec 1999, Page(s):75-79